Device and method for restoring cathode emission in a thermionic electron tube

ABSTRACT

A variable, alternating current cathode emission restoring voltage is applied to the cathode and control grid electrodes of a cathode-ray tube, while a variable filament voltage is applied to the tube filament. The emission current waveform is displayed on an oscilloscope to enable a combination of emission restoring cathode-grid and filament voltage values and corresponding time durations to be set in response to the observed emission characteristics of the tube.

United States Patent Kozicki 5] Oct. 28, 1975 DEVICE AND METHOD FOR RESTORING 2,897,435 7/1959 P151611 316/2 x CATHODE EMISSI I A THERMIONIC 3,076,140 l/1963 Smith 324/158 R 3,641,391 2/1972 Badewitz 316/28 ELECTRON TUBE [75] Inventor: Harry Kozicki, Atlanta, Ga. primary Examiner Roy Lake [73] Assignee: RCA Corporation, New York, NY. Examinepdames Davie Attorney, Agent, or Firm-Edward J. Norton; William [22] Filed: Mar. 28, 1974 Squire [21] Appl. N0.: 455,902

[57] ABSTRACT 52 US. Cl. 316/2; 316/28; 324/24; A variable, alternating Current Cathode emission 324 25 storing voltage is applied to the cathode and control [51] Int. Cl. HOlJ 9/50 grid electrodes of a Cathode-ray tube, While a variable [58] Field of Search 316/2, 28; 324/24, 25, filament voltage is pp to the tube filament The 324 2 27 121 R, 15 R emission current waveform is displayed on an oscilloscope to enable a combination of emission restoring 5 References Cited cathode-grid and filament voltage values and corre- UNITED STATES PATENTS sponding time durations to be set in response to the observed emission characteristics of the tube. 2,717,190 9/1955 Shoup 316/2 2,774,645 12/1956 Batchelor, Jr. 316/2 7 Claims, 2 Drawing Figures I OSCILLOSCOPE H C V 0 0 US. Patent Oct. 28, 1975 Fia. l

VOLTAGE Fia. 2

DEVICE AND METHOD FOR RESTORING CATHODE EMISSION IN A THERMIONIC ELECTRON TUBE Background of the Invention Restoration of cathode emission of thermionic elec tron tubes, particularly cathode-ray tubes as used in the television industry, has involved a large variety of restoration techniques. These techniques include the applilo a light bulb or meter in the circuit. The light bulb tends to get brighter with improved cathode emission, and the meter indicates the RMS cathode-grid emission current. However, none of these techniques have been completely satisfactory in that there are a number of variables that may affect emission characteristics of a particular tube. In spite of these variables, the apparatus of the prior art all attempt to apply the same voltages, currents and same time durations within the limitations of a particular apparatus. Hopefully, the voltages and currents, and time durations set up for an apparatus in use are sufficient for the tube being restored. However, this is not always the case. Some tubes tend to be overdriven and destroyed, while some tubes are not capable of restoration. This is not readily observable on the apparatus. Some tubes may be restored by increasing the heater voltage of the tubes, by increasing the grid to cathode current, or by some combination of these, either below, at or above operating potentials. The exact operating potentials are usually fixed by the characteristics of the test apparatus itself. However, none of these apparatus indicate the true condition of the tube under test or the actual effects of the restoration process on the tube.

Summary of the Invention An apparatus is provided for use with a waveform indicating device. The apparatus restores the electron emission of the cathode of a thermionic electron tube having a filament, cathode and grid electrodes. The apparatus comprises means for providing an alternating voltage having a selected value anywhere within a first given range and a selected time duration anywhere within a second given range. Circuit means are arranged to apply the alternating voltage to the grid and cathode electrodes to produce a cathode restoring current between the cathode and grid electrodes. The circuit means provides a first voltage manifesting the restoring current and a second voltage manifesting the restoring voltage corresponding to the restoring current. Interconnect means removeably connects the waveform indicating device to the circuit means to provide an indication of the instantaneous value of the restoring current manifested by the first and second voltages when the waveform indicating device is connected to the circuit means. With the indication so provided, the proper alternating voltage value and time duration tending to restore the electron emission of the cathode in response to the instantaneous value of the restoring current can be selected.

A method of rejuvenating the cathode electron emission of a thermionic electron tube having cathode, grid and filament electrodes comprises the steps of providing an alternating voltage having a selected value anywhere within a first given range and a selected time duration anywhere within a second given range, producing a cathode restoring current between the cathode and grid electrodes by applying the alternating voltage to the grid and cathode electrode; observing the instantaneous value of the restoring, current as a function of the voltage applied to the grid. and cathode electrodes; and varying the voltage and time duration within the ranges in accordance with the observed relationship of the instantaneous restoring current value to the gridcathode voltage.

In the Drawings FIG. 1 is a circuit diagram of a cathode emission restoring apparatus embodying the present invention. and

FIG. 2 is a group of waveforms useful in explaining the embodiment of FIG. 1.

Detailed Description In FIG. 1, a portion of a television picture tube 10 is shown in dotted outline and includes three color cathode-ray tube guns. The blue gun has a filament I2, cathode l4 and control grid 16. The green gun has a filament 18, a cathode 20 and a control grid 22. The red gun has a filament 24, a cathode 26 and a control grid 28. Each of the filament, control grid and cathode electrodes are connected to corresponding terminations, not shown, projecting from the television tube. To electrically couple the television tube 10 to the apparatus 11 of the present invention, suitable mating female connectors (not shown) are associated with the apparatus 11. These female connection devices are well known and no further description need be made here.

The apparatus 11 of FIG. I includes an autotransformer 30 which is coupled to a source of alternating voltage V such as normal household voltage. A variable resistance 32 is coupled across the windings of autotransformer 30 to vary the output voltage applied at secondary winding 34 in the range of O to 100 volts alternating current, and to limit the current through tube 10 during the restoring process. Winding 34 provides an output voltage between apparatus 11 output terminals 40 and 42. One side of winding 34 is coupled to output terminal 40 through resistance 43 while the other side is connected directly to output terminal 42. Across winding 34 are serially connected resistances 43, 44 and 46. The junction of resistances 44 and 46 is connected to apparatus 11 output terminal 48. The junction of winding 34 with resistance 43 is connected through leads 50, 52 and 54 to the respective red, green and blue control grids 28, 22 and 16 of tube 10. Terminal 48 is connected to the cathode 14 through switch 56, to cathode 20 through switch 58, and to the cathode 26 through switch 60. Filaments 12, I8 and 24 are connected in parallel to a source of voltage V; through a variable resistance 62 and transformer 68. Resistance 62 varies the output voltage across transformer output terminals 64 and 66. Suitably calibrated transformer 68 provides the voltage between terminals 64 and 66 at a value which varies from below normal to above normal operating filament voltage levels, preferably from O to about 12 volt alternating current. Terminals 40, 48 and 42 are respectively connected to the horizontal, common and vertical deflection input terminals of a conventional oscilloscope 7.

In operation, the red, blue and green guns of television picture tube are connected to apparatus 11 by way of the respective control grid, cathode and filament electrodes. It should be understood that the apparatus of the present invention is provided with a number of different connectors arranged to accommodate connections to the many different types of television picture tubes.

With the filament voltage at zero across terminals 64 and 66 and the restoring voltage across winding 34 of transformer at zero, resistance 32 is slowly varied to increase the voltage across winding 34 between 0 and 100 volts, preferably to a magnitude in the range of about 50 to 75 volts. The voltage may also be shifted in value by displacement of wiper arm 31 of autotransformer 30. With a voltage applied across winding 34, emission current appears in resistance 46 when any of switches 56, 58 or 60 is closed. Only one of switches 56, 58 or 60 is closed at one time to effect restoration of the corresponding gun. At this time, a voltage appears across resistances 44 and 43 which voltage corresponds to the voltage across the grid and cathode electrodes. Resistances 43 and 44 form a voltage dividing network to provide a low voltage across resistance 44 as an input to the horizontal circuit of oscilloscope 70 via terminals and 48.

The voltage appearing across resistance 44 and the voltage appearing across resistance 46 are graphically plotted by oscilloscope 70. The type of waveform appearing on oscilloscope 70 is illustrated in FIG. 2. In FIG. 2, waveform (a) represents the poorest emission current and waveform (b) represents acceptable emission current. Waveforms (c), (d) and (e) represent other forms of poor emission current. The cooridinate labeled current" represents the voltage developed across resistance 46 while the coordinate labeled voltage represents the voltage developed across resistance 44.

As a result, the exact emission characteristic of the gun under test is readily observed on the oscilloscope 70. The voltage applied to the grid and cathode electrodes as well as the voltage applied to filaments being independently variable may be set at any value for any time duration to provide a current that approaches maximum emission current as represented by the waveform (b). Further, a weak tube that is not capable of being restored can readily be detected to prevent further possible damage to the picture tube by futile attempts to restore the emission thereof. By observing the emission waveform represented by the graph of FIG. 2, any changes in the emission characteristics of the gun under test is immediately detected and related to a given combination of voltages across the cathode, grid electrodes and filament and the corresponding time duration of these voltages.

As an example, assume in FIG. 2 waveform (a) represents the waveform of the emission characteristics of cathode 26 and grid 28. To restore the tube emission, variable resistance 32 of transformer 30 is adjusted to increase the voltage applied to the grid and cathode electrodes of that gun. Should the emission characteristics be fully restored, then the emission characteristics will appear as in waveform (b) of FIG. 2. If as a result of increasing the voltage across the grid and cathode electrodes, waveform (0) appears as the emission char- 4 acteristics, then other steps may be taken to further improve the emission characteristics of that gun.

In this regard, the voltage of transformer 30 may be reduced and a filament voltage applied across terminals 64 and 66 may be applied to the filament 24. Assume this voltage is less than normal operating voltage. The voltage across coil 34 is then increased to the level it was previously, and the Waveform of FIG. 2 observed again on oscilloscope 70. If no change in waveform (c) occurs, then the filament voltage across terminals 64 and 66 is increased to normal or above normal as the case may be while at the same time the operator observes the characteristics of waveform (c) to see if any further changes take place.

In some instances, the restoring voltage applied to the grid and cathode and to the heater filaments may deteriorate the tube, and the change in waveform (c) may go toward the characteristics displayed by waveform ((1). As a result, the heater and grid-cathode voltages may be immediately shut off by the operator by releasing or opening switch 60. It is thus evident that the time duration and magnitudes of the voltages applied both to the filament 24 and across the grid 28 and cathode 26 electrodes of the red gun may be determined almost instantaneously as the restoration process continues in response to the observed waveform characteristics. Consequently, unlimited combinations of voltage applied to the grid and cathode electrodes and voltage applied to the filament electrode may be pre-selected in any combination of values to provide an emission characteristic waveform that most closely approaches waveform (b) of FIG. 2.

Normal filament or heater voltage is usually around 6.3 volts. However, in restoring the emission in the cathode and grid electrodes, this voltage may be increased to about 12 volts. Damage to the tube, by the application of greater than normal operating potentials to the grid and cathode electrodes and the filament electrodes, is prevented by the observation of the emission characteristic waveform displayed by oscilloscope 70 and immediately shutting off the restoring signal to the television picture tube gun when the waveform appears to deteriorate or shows no sign of improvement. Observation of the actual emission current waveform permits a wider degree of flexibility in providing improved cathode emission or restoration than the use of light bulbs and meters as provided in prior art techniques. That is both the amplitude of the heater voltage, the grid to cathode voltage and the time duration thereof applied to the particular gun under test, have their effects almost instantaneously observed on the oscilloscope permitting a greater degree of flexibility than otherwise provided. Not all tubes require the same level of heat and grid to cathode voltage combinations and time durations to effect rejuvenation. In some cases, the voltage levels which are good for one tube will .be effective to destroy another tube. Observing the waveform, the destructive voltages may be removed from the circuit prior to permanent damage to the tube.

As a result, the voltage applied across the grid 28 and cathode electrode 26 by transformer 30 may be varied anywhere in the preferred emission restoring range. The time duration may be selectively controlled either by variable resistance 32 or by switch 60 in accordance with the behavior of the emission waveform as illustrated in FIG. 2.

Upon completion of the restoring test of the red gun, the test is continued in a similar manner as described above with respect to the green and blue guns. The characteristics of each of the waveforms thus may be set independently of the remaining guns. Thus, where only one gun is bad, as shown by one of waveforms (a), (c), (d) or (e) appearing on oscilloscope 70 when each gun is tested, only that one gun need be acted upon by apparatus 11.

Of course the restoring device described above may also be used to restore electron emission of a single cathode of a black and white television picture tube or any electron tube device. In such instance, the device is connected to the picture tube or any electron tube device by an appropriate connector (not shown) which connects the filament to terminals 64 and 66, the cathode to switch 60 and the grid to lead 50. The procedure for checking and restoring the electron emission is as described above.

What is claimed is:

1. An apparatus for use with a waveform display device, said apparatus restoring electron emission of the cathode of a thermionic electron tube having filament, cathode and grid electrodes, said apparatus comprising:

means arranged for providing an alternating voltage having a selected value anywhere within a first given range and a selected time duration anywhere within a second given range,

circuit means arranged to apply said alternating voltage to said grid and cathode electrodes to produce a cathode restoring current between said cathode and grid electrodes, said circuit means including means for providing a first voltage manifesting said restoring current and a second voltage manifesting a restoring voltage corresponding to said restoring current,

interconnect means for removeably connecting said device to said circuit means, said device indicating the instantaneous value of said restoring current manifested by said first and second voltages when said device is connected to said circuit means, and means for selecting the values of said alternating voltage and time duration thereof tending to restore the electron emission of said cathode determined according to said indicated instantaneous value.

2. The apparatus of claim 1 further including a filament voltage circuit arranged for connecting across said filament a voltage having a value anywhere within a third given range and including control means for set ting the filament voltage anywhere within said third given range.

3. The apparatus of claim 1 wherein said first voltage providing means includes a first resistance connected between said cathode electrode and said alternating voltage providing means, and said second voltage providing means includes a second resistance connected across said grid and cathode electrodes.

4. The apparatus of claim 3 wherein said second resistance includes a voltage dividing means coupled between said alternating voltage providing means and said interconnect means, said dividing means being arranged to provide a fourth voltage across said cathode and grid electrodes greater than said second voltage.

5. An apparatus for restoring electron emission of the cathode of a cathode-ray tube, comprising:

means including control means arranged for providing an electric potential between first and second terminals that varies from a first value to a second value, said control means selectively setting said second value anywhere within a given range,

a plurality of terminals each arranged to be selectively connected to a corresponding separate. different one of the cathode. control grid and filament electrodes of said tube,

a first resistance connected between the cathode electrode terminal and said first terminal of said potential providing means,

second and third resistances serially connected between the cathode and control grid electrode terminals,

means connecting the junction of said second resistance and said control grid terminal to said second terminal of said potential providing means,

switch means coupled between said third resistance and said cathode electrode terminal, and

an oscilloscope having horizontal and vertical inputs, said oscilloscope including means for connecting said horizontal input across said third resistance and means for connecting said vertical input across said first resistance to graphically display .the emission current of said tube when said varied potential is applied to said tube.

6. A method of rejuvenating the cathode electron emission of a thermionic electron tube having cathode, grid and filament electrodes comprising the steps of:

providing a voltage having a selected value anywhere within a first given range and a selected time duration anywhere within a second given range,

providing a cathode restoring current between said cathode and grid electrodes by applying said voltage to said grid and cathode electrodes,

observing the instantaneous value of the restoring current as a function of the voltage across said grid and cathode electrodes, and

varying said voltage and time duration within said ranges in accordance with the observed relationship of the instantaneous restoring current to said grid-cathode voltage value.

7. The method of claim 6 further including the steps of applying a voltage to said filament electrode and varying said filament voltage according to the observed restoring current waveform. 

1. An apparatus for use with a waveform display device, said apparatus restoring electron emission of the cathode of a thermionic electron tube having filament, cathode and grid electrodes, said apparatus comprising: means arranged for providing an alternating voltage having a selected value anywhere within a first given range and a selected time duration anywhere within a second given range, circuit means arranged to apply said alternating voltage to said grid and cathode electrodes to produce a cathode restoring current between said cathode and grid electrodes, said circuit means including means for providing a first voltage manifesting said restoring current and a second voltage manifesting a restoring voltage corresponding to said restoring current, interconnect means for removeably connecting said device to said circuit means, said device indicating the instantaneous value of said restoring current manifested by said first and second voltages when said device is connected to said circuit means, and means for selecting the values of said alternating voltage and time duration thereof tending to restore the electron emission of said cathode determined according to said indicated instantaneous value.
 2. The apparatus of claim 1 further including a filament voltage circuit arranged for connecting across said filament a voltage having a value anywhere within a third given range and including control means for setting the filament voltage anywhere within said third given range.
 3. The apparatus of claim 1 wherein said first voltage providing means includes a first resistance connected between said cathode electrode and said alternating voltage providing means, and said second voltage providing means includes a second resistance connected across said grid and cathode electrodes.
 4. The apparatus of claim 3 wherein said second resistance includes a voltage dividing means coupled between said alternating voltage providing means and said interconnect means, said dividing means being arranged to provide a fourth voltage across said cathode and grid electrodes greater than said second voltage.
 5. An apparatus for restoring electron emission of the cathode of a cathode-ray tube, comprising: means including control means arranged for providing an electric potential between first and second terminals that varies from a first value to a second value, said control means selectively setting said second value anywhere within a given range, a plurality of terminals each arranged to be selectively connected to a corresponding separate, different one of the cathode, control grid and filament electrodes of said tube, a first resistance connected between the cathode electrode terminal and said first terminal of said potential providing means, second and third resistances serially connected between the cathode and control grid electrode terminals, means connecting the junction of said second resistance and said control grid terminal to said second terminal of said potential providing means, switch means coupled between said third resistance and said cathode electrode terminal, and an oscilloscope having horizontal and vertical inputs, said oscilloscope including means for connecting said horizontal input across said third resistance and means for connecting said vertical input across said first resistance to graphically display the emission current of said tube when said varied potential is applied to said tube.
 6. A method of rejuvenating the cathode electron emission of a thermionic electron tube having cathode, grid and filament electrodes comprising the steps of: providing a voltage having a selected value anywhere within a first given range and a selected time duration anywhere within a second given range, providing a cathode restoring current between said cathode and grid electrodes by applying said voltage to said grid and cathode electrodes, observing the instantaneous value of the restoring current as a function of the voltage across said grid and cathode electrodes, and varying said voltage and time duration within said ranges in accordance with the observed relationship of the instAntaneous restoring current to said grid-cathode voltage value.
 7. The method of claim 6 further including the steps of applying a voltage to said filament electrode and varying said filament voltage according to the observed restoring current waveform. 